1. Field of the Invention
This invention relates to a process for producing a triglyceride mix free from components hampering further processing or a triglyceride of single fatty acids which is at least technically pure, from a vegetable oil and/or a derivative containing the unaltered carbon framework of a vegetable oil as starting material, which is cooled as such or in solution and then separated into a predominantly solid and a predominantly liquid phase, wherein the cooling and separation of one of the phases or both phases are repeated if desired.
In the further processing of triglyceride mixes, especially in double bond derivatives formed from the oleic acid of such mixes, it is particularly important that the mix to be processed does not contain any components which undergo reactions concurrent with the reaction of the double bond of the oleic acid component. On the other hand it is not necessary to isolate the oleic acid component completely for this purpose, which would lead to unacceptably high costs.
2. Description of the Prior Art
The majority of vegetable oils, especially the agriculturally produced vegetable oils, contain as fatty acids those with chain lengths of C16 and C18, the commonest fatty acids being palmitic acid (C16), stearic acid (C18), oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3). The numbers following the colons give the number of double bonds in the fatty acid chain.
Although the majority of common fats and oils consist mainly of triglycerides of these 5 fatty acids, they exhibit in part substantial differences in chemical and physical properties. These differences arise above all in that even with only moderately different fatty acid patterns, serious differences exist in the distribution of the individual triglycerides in the oils and fats involved.
With an oil or fat with a content of 50% of one predominant fatty acid in the fatty acid pattern, there are, in accordance with the combination rules, over 150 chemically different triglycerides present in appreciable proportions, if all the above-mentioned 5 fatty acids occur in appreciable proportions in the fatty acid pattern. The "main component" is merely the triglyceride carrying the predominant fatty acid. It is however represented by only 12.5% of the total amount of triglyceride. As against this, an oil or a fat in which one fatty acid is represented by approximately 80% in the fatty acid pattern, consists practically only of those triglycerides in which the predominant fatty acid occurs at least twice. Overall such an oil consists much more than 90% of merely nine different triglycerides, when all the above-mentioned five fatty acids are present in appreciable proportions in the fatty acid pattern. Over 50% of such a fat or oil is formed from the triglyceride carrying solely the predominant fatty acid.
From the above it is clear that--if possible at all--separation of chemically uniformly constituted triglycerides is more possible with such oils and fats as those in which a single fatty acid predominates strongly.
However, even in this case the art has previously taught that the differences in physical properties of the triglycerides in question are so small that separation of the triglycerides by simple physical methods of separation would not be possible.
The production of chemically pure oleic acid, linoleic acid and linolenic acid, as well as the production of chemically pure mono, di and triglycerides of these fatty acids has been effected to date by use of extremely expensive physical and chemical methods, such as high pressure liquid chromatography (HPLC) and the chemical synthesis of the mono, di and triglycerides from the corresponding fatty acids previously rendered pure. Accordingly it is true that highly enriched triglycerides of vegetable oils or their derivatives, containing only one fatty acid type can be produced but only at very substantial cost. These lie in order of magnitude of about 10,000 DM per kg for a trioleate of high purity. With the production of the pure fatty acids practiced to date, as also the pure mono, di and triglycerides, the expense of separation and synthesis so exceeds the raw material costs that the latter are practically insignificant. Accordingly, although inexpensive raw materials with high contents of the relevant fatty acids are available and although the above-mentioned fatty acids are very suitable on account of their chemical structure as chemical starting materials (e.g. for ozonolysis), chemically pure reactive fatty acids play no part in the industrial field of technology on account of the lack so far of the possibility of producing them in chemically pure form.
In what follows, the invention will be described using the example of such triglyceride mixes as contain oleic acid as an essential component. The invention can however be similarly employed with other triglyceride mixes.
Oleic acid represents one of the most important raw materials of oleo-chemistry as a whole. It occurs in vegetable and animal oils and fats, accompanied by a plurality of other saturated and unsaturated fatty acids of various chain lengths, in part multiple unsaturated, above all as triglycerides. As a rule, especially with the fats and oils of technological interest, the fatty acids with chain lengths between C.sub.12 and C.sub.22 predominate, the C.sub.18 fatty acids in turn being especially strongly represented.
Although a number of methods for converting oleic acid into reaction products are used industrially--one of the most important conversions of oleic acid is ozonolysis, in which the oleic acid in split by oxidation into azelaic acid and pelargonic acid--the raw material used for oleo-chemistry is not pure oleic acid by merely enriched oleic acid. As a rule, the concentration of oleic acid in the raw material amounts to 72 to 75%. Such enriched fractions are obtained from inexpensive tallow. It has been found that a higher enrichment than 72 to 75% oleic acid content in the reaction product cannot be implemented without renouncing the price advantage of tallow as raw material. The enrichment mechanism used for this also disproportionally enriches the many unsaturated fatty acids which may be present.
The object of the invention is therefore firstly to provide a process in which raw material is produced for the further processing of triglyceride mixes, especially for the derivative formation from the oleic acid components of such mixes, which contain the components of interest more strongly enriched and which moreover contain hardly any components which interfere with the further processing, especially no or hardly any multiple unsaturated fatty acids. Furthermore a process is to be provided capable of producing economically at least technically pure and preferable highly pure triglycerides, containing only a single fatty acid type, such as for example trioleate, from vegetable oils or their derivatives as starting materials.
Oil seeds have recently been grown in whose oils oleic acid in natively present in amounts of above about 80% ("high oleic oil"). The performance of reactions with the oleic acid is thus effectively facilitated. The stated limit of 80% is not to be regarded as rigid; thus sunflower oil with an oleic acid content of a little above 78% is likewise to be called a high oleic oil.